Refine duplicate arrow function parameter location handling

src/parsing/parser.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/parsing/parser.h"
 
 #include <memory>
 
 #include "src/api.h"
 #include "src/ast/ast-expression-rewriter.h"
@@ skipping 2591 matching lines @@
     return;
   }
 
   ExpressionClassifier classifier(this);
   if (!parameters->is_simple) {
     this->classifier()->RecordNonSimpleParameter();
   }
   for (int i = 0; i < parameters->Arity(); ++i) {
     auto parameter = parameters->at(i);
     DeclareFormalParameter(parameters->scope, parameter);
-    if (!duplicate_loc->IsValid()) {
+    if (!this->classifier()
+             ->is_valid_formal_parameter_list_without_duplicates() &&
+        !duplicate_loc->IsValid()) {
       *duplicate_loc =
           this->classifier()->duplicate_formal_parameter_error().location;
     }
   }
   DCHECK_EQ(parameters->is_simple, parameters->scope->has_simple_parameters());
 }
 
 void Parser::ReindexLiterals(const ParserFormalParameters& parameters) {
   if (function_state_->materialized_literal_count() > 0) {
     AstLiteralReindexer reindexer;
@@ skipping 2982 matching lines @@
 
   return final_loop;
 }
 
 #undef CHECK_OK
 #undef CHECK_OK_VOID
 #undef CHECK_FAILED
 
 }  // namespace internal
 }  // namespace v8